liblightdm-gobject: define common-user GIR type

[ousamabenyounes]

Summary

• annotate the internal common-user property with its concrete introspection type
• reject generated GIR files that contain unnamed <type> elements when xmllint is available
• detect xmllint at configure time and distinguish inspection errors from malformed type metadata

Test verification (RED → GREEN)

• RED check (same check with the production annotation removed): 1/1 new checks failed:

  $ make check DEBUG=true
  LightDM-1.gir contains an unnamed type
  make[2]: *** [Makefile:1039: check-local] Error 1
  

• GREEN check (same check with the annotation restored): 1/1 new checks passed:

  $ make check DEBUG=true
  Testsuite summary for lightdm 1.33.1
  # TOTAL: 352
  # PASS:  352
  # FAIL:  0
  # ERROR: 0
  

• pinned downstream parser reproduction: gtk-rs gir at 2ae5101 reports Missing name attribute on <type> element before the fix and no error after it

• full local suite, Ubuntu rolling: 352/352 passed

• full local suite, Fedora latest: 352/352 passed

Fixes #463

[jpeisach]

Hi,

I personally am a little uneasy about vibe coded contributions - I hope you understand that.

I am not going to close the PR outright, since that would be rude, and likely violate Ubuntu Code of Conduct. In the meantime, I will get some other opinions about a contribution policy to lightdm, and acceptable uses of LLMs.

I also am not sure that the PR would actually fix the problem, and I would go into detail, but again I'm not sure how I feel about it due to potential use of training.

I will get back to you. Let me know if you need anything.

Thanks :)

[jpeisach]

Hm.. I'm not sure if the xmllint is needed because the .gir files are generated automatically. I guess perhaps they could be a way of checking the output of the girs?

As for the type: It's now removed, and the gir tool isn't generating it... weird...

[jpeisach]

Well, it is internal anyway.

I'm going to hold onto this until I figure out whether it should or should not include the property at all if it's unused